THE MINOR PLANET BULLETIN OF THE MINOR PLANETS SECTION OF THE BULLETIN ASSOCIATION OF LUNAR AND PLANETARY OBSERVERS VOLUME 34, NUMBER 1, A.D. 2007 JANUARY-MARCH 1. A ROTATION PERIOD FOR 1493 SIGRID -0.2 Colin Bembrick 1493 SIGRID Mt Tarana Observatory -0.1 PO Box 1537, Bathurst, NSW, Australia 0 [email protected] 0.1 Jeff Byron 0.2 Cecil Sayers Observatory 22-Jul 0.3 18 Albuera Rd, Epping, NSW, Australia 26-Jul 27-Jul 0.4 29-Jul (Received: 9 October Revised: 30 October) 1-Aug 0.5 6-Aug 7-Aug 0.6 22-Aug Minor planet 1493 Sigrid was observed over 8 nights in 0.7 2006. The synodic period was found to be 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 43.296±0.048hr with a peak-to-peak amplitude of at least 0.6 magnitudes. The axial ratio a/b implied by the peak to peak variation is 1.74. compared with most asteroids of less than 50km diameter, which have mean rotation rates of 2-3 revs/day (Binzel et al, 1989). Minor planet 1493 Sigrid was observed over a period of 32 days References from two sites in NSW, Australia, Mt Tarana Observatory (S 33d 26.1m E 149d 45.4m +880m) and Cecil Sayers Observa- Barbera, R. (2004). “AVE” Analisis de Variabilidad Estelar, tory (S 33d 46.9m E 151d 05.1m +80m). The Cecil Sayers version 2.51. Grup d’Estudis Astronomics. Observatory utilizes a 20cm f/7 Newtonian reflector and http://usuarios.lycos.es/barbera/AVE/AveInternational.htm Cookbook CCD camera. The equipment of the Mt Tarana Observatory is described in Bembrick (2001). No data on this Bembrick, C. (2001). “Lightcurves and Period Determination for asteroid was found in the latest list of rotational parameters (Harris 1362 Griqua”. Minor Planet Bulletin 28, 42-43. & Warner, 2006). Binzel, R.P., Farinella, P., Zappala, V. and Cellino, (1989). The aspect data for the eight nights of observation are shown in Asteroid Rotation Rates. In Asteroids II (Binzel, Richard P., the table. Observations were made using unfiltered differential Gehrels, Tom and Matthews, Mildred Shapley, eds.) pp 416-441. photometry and all data were light time corrected. The aspect data Univ. Arizona Press, Tucson. table also shows the percentage of the lightcurve observed each night and PAB is the Phase Angle Bisector. Harris, A.W. and Warner, B.D. (2006). “Minor Planet Lightcurve Parameters”. Updated March 14, 2006. Period analysis was carried out using the “AVE” software http://cfa-www.harvard.edu/iau/lists/LightcurveDat.html (Barbera, 2004). The period derived for Sigrid appears to be the best fit to the available data, but note that full phase coverage has PAB PAB Phase %Phase not been achieved. A period of half the derived value gives a UT Date Long Lat Angle Coverage monomodal phase stack and this is thought to be less likely than 2006 Jul 22 305.7 -1.8 4.5 10 the bimodal light curve adopted herein. The arbitrary zero phase 2006 Jul 26 306.1 -1.7 2.3 12 2006 Jul 27 306.2 -1.7 1.8 8 maximum in 2006 is at JD 2453939.200. The 2006 composite 2006 Jul 29 306.4 -1.6 1.1 15 lightcurve for 1493 Sigrid has been compiled assuming a bimodal 2006 Aug 01 306.6 -1.5 2.0 5 lightcurve. The phase coverage is not complete and the period 2006 Aug 06 307.1 -1.4 4.8 15 determined could be modified with additional data. The peak-to- 2006 Aug 07 307.2 -1.4 5.4 16 peak variation of at least 0.6 magnitudes implies an axial ratio a/b 2006 Aug 22 308.8 -1.0 13.6 12 of 1.74. With a period of 43.296±0.048hr, Sigrid is a slow rotator Minor Planet Bulletin 34 (2007) Available on line http://www.minorplanetobserver.com/mpb/default.htm 2 LIGHTCURVE ANALYSIS OF 1495 HELSINKI Julian Oey Leura Observatory 94 Rawson Pde. Leura Australia [email protected] Raoul Behrend Observatoire de Genève CH-1290 Sauverny - Suisse Petr Pravec Astronomical Institute CZ-25165 Ondrejov Czech Republic Jean Paul Teng, Bruno Payet, and Yannick Leonie L ‘Observatoire des Makes that other observers from different longitude should be recruited to La Reunion Island help resolve the data further. (Received: 4 October) The combined effort from J.P. Teng et al. gave no indication of the variability shown in Oey’s earlier lightcurve. It was realized that an error may have occurred in Oey’s light curve data. An analysis This is a collective effort from observers at different of the more complete dataset has shown that all but two sessions longitudes to derive an accurate synodic period of fitted entirely with a single periodicity; the two unfitting sessions 5.33116±0.00003hr with amplitude of 0.83 and were 2006-5-8.6 and 13.6, both of the initial dataset of six nights. 0.61±0.03 mag in May and June 2006, respectively, for While the 5-8.6 session showed a higher amplitude, the 5-13.6 the minor planet 1495 Helsinki. session showed a shift in time. A revisit of the original images of the two sessions was obviously needed. Leura observatory is located about 100km west of Sydney Australia at an altitude of 950m. It houses a 0.35m Celestron At this time, a new version of Canopus reduction software Schmidt-Cassegrain Telescope operating at f/11. Attached to it is (Canopus V9.101) was released. It incorporated a new feature an SBIG ST9XE CCD camera which has a Kodak KAF-0261 with the ability to subtract nearby faint stars allowing data CCD giving 1.07 arc second/pixel at binning 1x1. No filters were contaminated with these faint stars useful. (Warner 2006). The used for all images. Dark frames and Flat Field frames were used data were then reduced once more and the revised data of 5-8.6 for image calibration. L ‘Observatoire des Makes is located in La fitted entirely with the single periodicity; the higher amplitude of Reunion Island in the Indian Ocean. It houses a 0.35m Celestron the first reduction of the night was caused by uneliminated Schmidt-Cassegrain telescope mounted on CDM mount with background stars. At that point, there remained the one unfitting MCMT II. Attached to it is an ST7 SBIG CCD camera and a focal session of 5-13.6, which showed a phase shift; when adding 0.010 reducer operating at f3.3. An 80x900 refractor telescope is piggy day to all times of the session, it fit well with all the other data. A backed on the main telescope along with an ST6 SBIG CCD re-reduction of the original images by Oey showed that there was which operates as an autoguider. a time error in the initial reduction; while a cause of the time error of the initial reduction was not revealed, the newly reduced data For data reduction, Oey used the Canopus V9 software where showed a perfect fit. So, the revisit has eliminated the serious differential photometry was employed whereas Teng et al. sent all reduction problems in the two sessions and it confirmed that there data to Behrend that were latter reduced and compiled in his web was only one periodicity present in the asteroid during the whole site (Behrend 2006). The composite lightcurves were then observational interval. combined and reproduced for this publicatiton. All data were merged by Behrend to obtain a lightcurve of period Asteroid 1495 Helsinki was originally selected due to its lack of 5.33116±0.00003hr with amplitude of 0.61±0.03 mag. It's worth published results. The work was started from Leura Observatory noting that the larger amplitude in early May was at around phase on 13 April 2006 and continued for six sessions that ended on 21 angle 22° and the smaller amplitude in late June was at about 12° May 2006. A month later, Behrend of Genève Observatory phase angle. contacted Oey regarding the merging of data by one of his contributors with the recently obtained data from Leura. After the References merge, the initial appearance of the curve was one that does not fit Warner, B. D. (2006). “StarBGone”. On Minor Planet Observer well into a clean bimodal curve. It was considered that the data website. http://www.minorplanetobserver.com/MPOSoftware/ may be caused by either a binary asteroid or a tumbling object. StarBGone.htm Communications were initiated with Pravec of Ondrejov Observatory. He had the opportunity to analyze Oey’s six Behrend, R. (2006), Observatoire de Genève web site. sessions data earlier on separate occasion; the initial data showed a http://obswww.unige.ch/~behrend/page_cou.html. complex behavior, with some of sessions having a larger amplitude and others being shifted in phase. No good solution could be found from the initial data, however, and he suggested Minor Planet Bulletin 34 (2007) 3 THE ROTATION PERIOD OF 562 SALOME Colin Bembrick Mt Tarana Observatory PO Box 1537, Bathurst, NSW, Australia [email protected] Bill Allen Vintage Lane Observatory 83 Vintage Lane, RD3, Blenheim, New Zealand (Received: 15 October) Minor planet 562 Salome was observed over 8 nights in Binzel, R.P., Farinella, P., Zappala, V. and Cellino, A, (1989). 2006. The synodic period was found to be Asteroid Rotation Rates. In Asteroids II (Binzel, Richard P., 12.705±0.006hr with a peak-to-peak amplitude of a little Gehrels, Tom and Matthews, Mildred Shapley, eds.) 416-441.